The present invention relates to steam generating furnaces and, in particular, to a buckstay design for use in supporting the tube walls of the furnace.
Steam boiler plants generally have large furnaces which are commonly constructed of a number of water-cooled tubes welded in side-by-side arrangement to form gas tight tube banks forming the walls of the furnace. These tube walls are generally supported from the top of the structural framework of the steam generating plant. As the furnace approaches operating temperature, the furnace walls expand vertically downward as well as tending to dish in a horizontal direction. Additionally, the pressure excursions within the furnace, either an increase or a decrease in pressure within the furnace, cause a resultant additional flexing of the tube walls either inwardly or outwardly in a horizontal direction. Therefore, it has become customary and necessary to provide an arrangement of flanged girder beams, typically referred to as buckstays, that extend around the furnace to provide additional support to the furnace walls and prevent the dishing of the furnace walls in a horizontal direction as affected by pressure differential.
Typically, these buckstays are disposed in bands around the parimeter of the furnace tube walls at vertically spaced intervals throughout the height of the furnace wall. Horizontally, the buckstays on opposite walls of the furnace are interconnected through buckstay ties so that the reactions of one buckstay are resisted by the reactions of the buckstay on the opposing wall so as to counteract the pressure forces acting on the furnace walls. Vertically, it has been customary to provide vertical support members to interconnect each buckstay to its upper and lower neighbors with a connection that permits a sliding action which is required due to relative movement between the furnace tube walls to which each buckstay is connected and the buckstays themselves. As the furnace expands differentially in a vertical direction, each level of buckstays would move a different amount under the influence of the vertical elongation of the furnace tube walls. This relative vertical expansion between the furnace tube wall structure and the buckstays would produce a very high localized bending moment on the buckstays which has been customary to relieve with these vertical support members which extend between neighboring buckstays. Arrangements for relieving or preventing the bending moment of this type are disclosed in U.S. Pat. No. 3,461,847 and U.S. Pat. No. 3,861,360.
In such a buckstay arrangement utilizing vertically extending support members for interlinking the neighboring elevations of buckstays and absorbing the bending moment, the structural system is necessarily massive and also somewhat rigid. Therefore, the structural support system has a certain amount of inertia which must be overcome before the structural system can flex properly in response to pressure changes within the furnace and thereby absorb the pressure forces acting of the furnace walls. In the event that there is a sudden change in furnace pressure, an explosive or implosive load may be exerted on the furnace tube walls over a very short period of time. In such a system as described above wherein the bands of buckstays are interconnected in a vertical direction, it has been observed that the buckstay system may in some instances be incapable of responding to such a sudden change in furnace pressure without permanent damage to the buckstay system and/or the furnace wall.
Therefore, it is the object of the present invention to provide a buckstay design wherein the need for a vertical interconnection between adjacent bands of furnace buckstays is not necessary.
It is a further object of the invention to provide a buckstay having a cross-section which provides an inherently high polar high moment of inertia for resisting bending moments on the buckstay.
It is a further object of the invention to provide a buckstay having a cross-section which provides an inherent high polar moment of inertia to furnish lateral stability for buckling.